The present invention relates to an air circuit breaker coil adapter for adapting an air circuit breaker, and to a method of adapting an air circuit breaker utilising a cylindrical or substantially cylindrical operating coil unit to a non-cylindrical operating coil unit.
An air circuit breaker is an electric circuit protection device which is installed between an electric source or supply and load units or devices to be operated. The breaker protects the load unit and a load line from an abnormal current generated on the electric circuit. The breaker also performs a distribution function for changing the electric power line to another line.
The electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The power is then routed through overcurrent protection devices to designated branch circuits supplying one or more loads. Electrical power distribution systems and their components require protection from numerous types of malfunctions, including overcurrent conditions, overvoltage conditions, undervoltage conditions, reverse current flow, and unbalanced phase voltages. These overcurrent devices are typically circuit interrupters such as circuit breakers and fuses which are designed to interrupt the electrical current if the limits of the conductors supplying the loads are surpassed and thus a malfunction condition is detected. Interruption of the circuit reduces the risk of injury or the potential of property damage from a resulting fire.
More elaborate time-current trip characteristics have been developed, such that a circuit breaker can rapidly open upon very high current with the time delay being roughly inversely proportional to the degree of overload. Circuit breakers are a preferred type of circuit interrupter, since a resetting mechanism allows their reuse. Circuit breakers can interrupt an electric circuit due to a trip condition such as a current overload or ground fault. The current overload condition results when a current exceeds the continuous rating of the breaker for a time interval determined by the trip current.
Circuit breakers are mechanical switching devices capable of making, carrying, and breaking currents under normal circuit conditions and also making, carrying for a specified time, and breaking currents under specified abnormal conditions such as those described above. Basically, a circuit breaker comprises a pair of separable contacts, an operating mechanism for effecting separation of the contacts, and a tripping mechanism which automatically releases the operating mechanism upon the occurrence of an overload or fault condition. The medium in which circuit interruption is performed may be designated by a suitable prefix, for example, air-blast circuit breaker, gas circuit breaker, oil circuit breaker, or vacuum circuit breaker. In operation, a circuit breaker is opened by energizing a trip coil associated with the circuit breaker. Once the trip coil is energized, the main contacts are opened and then auxiliary contacts are opened to prevent damage to the trip coil.
Circuit breakers may include an electronic trip unit that senses electrical current to the protected equipment. If the sensed electrical current indicates an overcurrent situation, the electronic trip unit provides a trip signal to a trip actuator. In response to the trip signal, the trip actuator actuates a mechanical operating mechanism. Actuation of the mechanical operating mechanism by the trip actuator causes the mechanical operating mechanism to separate the electrical contacts, stopping the flow of current to the protected equipment.
Air circuit breakers include operating mechanisms that are mainly exposed to the environment, hence the use of the term ‘air’. Since an air circuit breaker is rated to carry several thousand amperes of current continuously, the exposure to convection cooling air assists in keeping the operating components within reasonable temperature limits.
A typical air circuit breaker comprises a component, module or unit for connecting an electrical power source to an electrical power consumer or load. The component may be referred to as a main contact assembly, and the main contact is typically either open, interrupting a path for power to travel from the source to the load, or closed, providing a path for power to travel from the source to the load.
In many air circuit breakers, the force necessary to open or close the main contact assembly is provided by an arrangement of compression springs, and the mechanism for controlling the compression springs comprises a configuration of mechanical linkages between a latching shaft and an actuation device. The actuation device may be manually or electrically operated. The current invention is for use with an air circuit breaker which utilises one or more, and typically three, electrically operable solenoid coil units as the said actuation devices.
Such air circuit breakers are critical for large scale power distribution systems, and in many cases it is not only cost-prohibitive to install an upgraded breaker system, but the down time for such a major removal and reinstallation program is unsupportable thereby making the process practically impossible.
Additionally, manufacturers are known to scale down factory support for existing air circuit breakers, forcing the consumer along the upgrade route or having the consumer wait unacceptably long periods for bespoke production of individual parts. New model components are typically not compatible with existing older model components, thus forcing the consumer to upgrade the entire breaker which in many cases is unacceptable as described above.
One of the main breakage areas and therefore replacement requirements of an air circuit breaker is the operating coil unit. In particular, the widely installed and now obsolete Merlin Gerin® Masterpact® M air circuit breaker utilises substantially cylindrical operating coil units. However, the newer NW model utilises physically incompatible substantially cuboid operating coil units. The present invention therefore seeks to provide a solution to at least part of this problem by providing an operating coil unit adapter.